PURPOSE: To leave a sufficient area of a flat part while a fault due to a bulk wave is sufficiently eliminated by arranging rectangular holes side by side at a prescribed interval in lengthwise directions and arranging each column of the rectangular holes so that unprocessed parts among the holes are not overlapped in the propagation direction of a surface wave.

CONSTITUTION: Lots of very thin and long rectangular holes 1 are provided to a side of a piezoelectric single crystal substrate opposite to its electrode forming side. The rectangular holes 1 are provided so that the lengthwise direction is in crossing with at least the propagation direction of a surface wave. The lots of the rectangular holes 1 are arranged in a form of plural hole arrays 2a-2e whose lengthwise directions, for example, are arranged in a line and which are arranged at a prescribed interval, and the plural hole arrays 2a-2e are arranged so that unprocessed parts 3 between the rectangular holes 1 of adjacent columns are not overlapped with respect to a propagation direction X of the surface wave. Thus, the propagation of an undesired wave (disturbing wave) such as a bulk wave is prevented effectively and the area of the rectangular holes 1 is reduced.